Square and Triangle Op-Amp Oscillator

Here is the circuit of a
Op-Amp based Square Wave Generator. One of
the main application of this is in a Simple PWM
circuit and Triangle Opamp Oscillator. The Slope
of the Triangle wave is compared with a DC Level
to derive a pulse width or On-Time proportional to
a Voltage.

This On-Time proportional to voltage is for a
fixed oscillation rate based on C2-C3 and R15. The
C2-C3 form a Unpolarized cap, This type is also
used in crossover networks in speaker boxes. This
is because, a plastic 4.7 uF (2 * 10uF series) is
big and costlier, but a plastic cap is very stable
and closer to an ideal cap.

First you need to know that most opamps in such
circuits can give a square wave, but very few can
swing to the rails (+/-5). For designing take 75%
of Vcc.
CA3130 is one that can swing to rails like a
CMOS gate.

Assuming the swing of output is around +/- 4V,
the pin 10 + input will be at +/- 2V. When the cap
is discharged at 0 V, let us take that the output
is +, the cap charges to a little above +2, -
input becomes dominant, so output swings negative.
This discharges the cap to 0 and then charges it
negatively upto -2. This in turn flips the output
to + as pin 10 turns dominant. Hence this
continues as a oscillation, with a nice triangle
across the cap for the PWM comparator.

Dominant means more +, 0 is positive compared to
-2V. Also -2.5 is negative compared to -2.2.

Generic Circuit Diagram of a Op-Amp based Square
Wave Generator. Use it as a Simple PWM circuit or
Triangle Opamp Oscillator.Used in A to D Convertors,
Switchers and Communications .